Process for forming carton bottom



United States Patent 3,303,760 PROCESS FOR FORMING CARTON BOTTOM Lawrence S. Tobias, Valley Stream, N.Y., assig'nor to International Paper Company, New York, N.Y., a corporation of New York No Drawing. Filed Apr. 6, 1964, Ser. No. 357,786 2 Claims. (Cl. 93-441) This invention relates to the bottoming of paperboard cartons. More particularly, it relates to a method of providing a leak-proof bottom for a plastic-coated paperboard container for liquids.

Plastic-coated, paperboard milk cartons, including the gable-topped variety sold under the trademark Pure-Pak have come a great distance in eliminating the use of glass bottles for the same purpose. They are light-weight, inexpensive, disposable, and, of course, safe insofar as they are shatter-proof.

Further, great advances have been made in making plastic-coated, paperboard milk cartons leak-proof. Socalled top-leakers have been substantially reduced in numbers by the incorporation in the cartons of developments such as those covered by co-pending Serial Nos. 201,899, filed June 12, 1962, now abandoned; 231,532, filed October 18, 1962, now Patent No. 3,178,089; 261,806, filed February 28, 1963, now abandoned; and, 266,325, filed March 19, 1963, now Patent No. 3,178,- 091. And, by the adaptation of closures shown, for instance, in U.S. Pats. Nos. 2,307,913, 2,439,768, and, 3,069,062, these cartons have been given bottoms of heightened integrity as shown in U.S. Pats. Nos. 3,120,- 333 and 3,120,335.

Nevertheless, the bottom of a plastic-coated, paperboard milk carton of current commercial design is the area of its greatest susceptibility to stress and strain, principally because paperboard has a tendency to rupture where bent or folded, and additional improvements in this connection are desirable. Accordingly it is an object of the present invention to overcome the problems presented by the milk carton bottom of current usage and to provide a design which is not prone to the same weaknesses.

It is old in the art to place preformed plastic lids, covers, or caps on containers made from wax-coated paperboard. See, for example, U.S. Pats. Nos. 2,623,685 and 2,638,261. It is also old in the art to form a plastic shield about the top of a wax-coated paperboard container. See, for instance, U.S. Pat. No. 2,197,739. Or to form in situ a plastic-coated paperboard top or bottom for a container of the same material. See, for example, US. Pat. No. 2,704,179. And, more recently, a manually operated device which forms plastic top and bottom closures for paperboard or plastic tubular containers from fiat closure blanks was disclosed. See U.S. Pat. No. 3,007,653. But such prior art does not adequately cope with the problem here contemplated wherein plasticcoated cartons needing more secure and leak-proof bottoms are mass-produced (i.e., erected, filled, and closed in the millions, if not billions) by dairies, fruit juice producers, or petroleum companies all over the World using standardized equipment and carton blanks.

In currently operating commercial installations, milk cartons, or similar containers of the type here involved, are made in accordance with a sequence of steps, and utilizing the mechanisms, described and depicted more fully in column 16 and FIGURE 32 of U.S. Pat. No. 3,002,328. Put simply, the manufacturer of such cartons or containers begins with withdrawing blanks therefor from a magazine by an appropriate loading mechanism and squaring the blanks to a rectangular cross-section. The squared blanks are placed upon a rectangular mandrel and, at substantially the same time, the bottom 3,303,760 Patented Feb. 14, 1967 closure flaps are subjected to an initial creasing or preclosing operation to produce a blank with partially folded bottom flaps. After receiving a square container blank, the mandrel rotates to carry the container, with its bottom closure flaps projecting outwardly from the end of the mandrel, through a heating tunnel Where the plastic, e.g., polyethylene, coating on the bottom closure flap surfaces of the container is raised to a temperature sufliciently high to cause it to melt. The heated bottom closure flaps are then folded together and the inner bottom flap inserted into position beneath the outer bottom flap by an appropriate tucking finger. Following the tucking op eration, a sealing pressure is applied to the closed and heated bottom flaps by suitable pressure pads to cause the plastic on adjoining flaps to adhere together and seal any crevices formed between the flaps to provide a liquidtight seal. The erected container having a closed bottom end is placed in a basket which is then immersed in a bath of near-boiling water. The water bath sterilizes the containers which are then placed open end up on a conveyor which carries them through a filling and sealing mechanism.

In accordance with the present invention, the container blanks are drawn from a magazine squared into a rectangular cross-section, and placed upon a rectangular mandrel in much the same way as it is now done. But the container blank of the present invention has no bottom closure flaps to be creased initially or preclosed and rides on the mandrel with its common bottom edge or with each bottom edge of each of its side walls projecting outwardly from, and disposed a short distance beyond, the end of the mandrel. Then, as the mandrel rotates to a bottoming station unit, the bottom edges of the container are uniformly made to come into a parallel relation with a suitably-held piece or small flat sheet of thermoplastic material (such as polyethylene or any of those listed in or suggested by U.S. Pat. No. 3,067,653) of predetermined thickness which is sufiiciently heated to permit the embedding of the carton bottom edges in the thermoplastic material without hazard of rupturing it when the sheet or bottom closure blank is brought, urged or pressed into contact with such edges by a movement of the blankholding device relative to, and along the axis of, the machine mandrel. Once the union between carton and bottom is completed, the bottom is both cooled and released from the device, which retracts. The machine mandrel then carries on with the normal manufacturing cycle.

The embedding impregnates the edges of the container with thermoplastic material, so as to form a tight bond between it and the individual cellulosic fibers of the car tons paperboard (as well as with the cartons coating material) and, when successfully achieved, can reduce the amount of thermoplastic material required in making the bottom blanks. For, when the aforesaid bond is truly formed, there is no need for oversize dimensions in the closure blank, as are suggested by both U.S. Pats. Nos. 2,704,179 and 3,067,653, to enable the formation by folding or crimping of bottom closure flanges and no need for beads on the carton bottom edges, as is suggested by U.S. Pat. No. 3,067,653, to permit a bottom closure clamping or snap-locking. These features are still useful, bu they are no longer necessities.

The equipment with which the method of the present invention can be performed will be the subject of a subsequent patent application. But it is obviously somewhat like that of U.S. Pat. No. 3,067,653, albeit highly automated, quick, and precise. And, unlike those shown in U.S. Pat. No. 3,067,653, its heating elements are not disposed to heat mildly the periphery of the thermoplastic bottom closure blanks, so as to enable the bending of the blanks at their circumference. Rather, they are disposed at points and at such a setting as to soften the blank ade quately where needed for the desired purpose of embedding the carton bottom edges therein.

To sum up, then, the present invention encompasses the in situ formation of a plastic bottom for a COntainer such as a plastic-coated paperboard, gable-topped carton in the course of its progress from being a fiat carton blank to being an erected, filled, and closed container of milk or some other fluid. It involves a method of employing portions of the carton, i.e., its bottom edges, as male molding elements in the formation of the carton bottom from a thermoplastic blank or, in other Words, of employing the carton as mandrel or core for the bottom (just as the machine mandrel is the core for the carton) and it involves employing the natural bottom edges or the cellulosic fibers making them up as the lineof purchase or sealing of the carton and its bottom, rather than employing the carton side walls or a built-up bead on such edges to do the job.

What is claimed is:

1. In the manufacture of paperboard cartons from fiat carton blanks, a method comprising a first step of handling a blank to provide a carton having sides ending in a common edge, a second step of placing the carton on a mandrel with the common edge extending beyond the mandrel, a third step of rotating the mandrel to a carton bottoming station, and a fourth step of pressing a fiat, heated blank made from a thermoplastic material against the common edge until it is embedded in the material.

2. In the manufacture of gable-topped, four-sided, thermoplastic-coated paperboard cartons for containing liquids, a method comprising a first step of squaring a blank to provide a carton having four sides ending in a common edge and a rectangular cross-section, a second step of placing the carton on a rectangular mandrel with the common edge extending beyond the mandrel, a third step of rotating the mandrel to a carton bottoming station, and a fourth step of pressing a fiat, heated blank made from a thermoplastic material against the common edge until it is embedded in the material.

References Cited by the Examiner UNITED STATES PATENTS 2,784,901 3/1957 Wilcox 2295.5 X 2,809,399 10/1957 Mead et al. 264249 X 3,002,328 10/1961 Monroe et al. 3,030,255 4/1962 Winston. 3,067,653 12/1962 Lesser et al. 9339.1

BERNARD STICKNEY, Primary Examiner. 

1. IN THE MANUFACTURE OF PAPERBOARD CARTONS FROM FLAT CARTON BLANKS, A METHOD COMPRISING A FIRST STEP OF HANDLING A BLANK TO PROVIDE A CARTON HAVING SIDES ENDING IN A COMMON EDGE, A SECOND STEP OF PLACING THE CARTON ON A MANDREL WITH THE COMMON EDGE EXTENDING BEYOND THE MANDREL, A THIRD STEP OF ROTATING THE MANDREL TO A CARTON BOTTOMING STATION, AND A FOURTH STEP OF PRESSING A FLAT, HEATED BLANK MADE FROM A THERMOPLASTIC MATERIAL AGAINST THE COMMON EDGE UNTIL IT IS EMBEDDED IN THE MATERIAL. 